<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    // let a = 1;
    // console.log(a);

    // var a = 1;
    // var a = 10;

    // let a = 1;
    // let a = 10; // Uncaught SyntaxError: Identifier 'a' has already been declared

    /*
        var:
            1. var可以重复声明

        let:
            1.同一作用域不能重复声明
     */
</script>
</body>
</html>
